The present invention relates to an optical device for deflecting a light beam, such as a laser beam for example.
A known beam deflector comprises a pair of wedge prisms positioned in the path of an incident beam of light, whose direction of propagation defines an optical axis. By virtue of refraction of the light beam upon passage through the prisms, each of the wedge prisms deflects the light beam in a direction transverse to the optical axis. When the prisms are mutually adjacent, and so aligned that the directions in which they deflect the light are parallel and mutually opposing, the light beam will pass through the prisms substantially undeviated. Relative rotation of the prisms about the optical axis will result in a net deviation of the light beam, whose magnitude depends upon the magnitude of the aforementioned relative rotation. The rotational displacement of the direction of any deviation of the light beam about the optical axis may be adjusted by a simultaneous rotation of the two wedge prisms once the relative rotation has been accomplished. Wedge prisms of this type must have very closely matched refractive indices, and substantially identical geometry (to within arc seconds) in order to ensure that the resulting beam deflector does not have a blind spot i.e. a given angle of deflection (or, more commonly the undeviated transmission of a light beam through the beam deflector) which is unattainable as a result of the prisms not being adequately matched.
The present invention seeks to ameliorate the difficulty and/or expense of producing two such closely matched prisms, and provides, according to a first aspect, a device for deflecting a light beam having a direction of incident propagation which defines an optical axis, the device being adapted to deflect the light beam away from the optical axis and along a deflected axis which is non-parallel to the optical axis, the device comprising first, second and third optical elements situated in the beam path, at least two of which are rotatable relative to the light beam to adjust deflection of the beam, wherein the geometry and refractive index of the optical elements is such that deflection of the light beam is adjustable throughout a predetermined solid angle about the optical axis.
Preferably the first and second optical elements have substantially similar geometries and refractive indices, and interact with the light beam to deflect the beam away from the optical axis in first and second directions of refractive deviation respectively, and the third optical element which interact with the light beam to deflect the beam away from the optical axis in a third direction of refractive deviation, wherein the geometry and refractive index of the third optical element relative to the geometry and refractive index of the first and second optical elements is such that: when the first and second optical elements are aligned about the optical axis such that the first and second directions of refractive deviation extend at notional angles of 0xc2x0 and xcex1xc2x0 respectively, the third direction of refractive deviation extends at a notional angle of [180+(xcex1xc2x0/2)], and the first second and third directions of refractive deviation are orthogonal to the optical axis, the light beam passes through the device with its path substantially undeviated, and wherein the first and second optical elements are rotatable relative to the optical axis to adjust deflection of the light beam.
The requisite refractive characteristics of the third optical element relative to those of the first and second optical elements may be attained by virtue of a geometry which differs from that of the first and second elements, or by virtue of a refractive index which differs from that of the first and second optical elements, or by virtue of a combination of a variation in both parameters.